In-situ thermally-reduced graphene oxide/epoxy composites: thermal and mechanical properties

Graphene has excellent mechanical, thermal, optical and electrical properties and this has made it a prime target for use as a filler material in the development of multifunctional polymeric composites. However, several challenges need to be overcome in order to take full advantage of the aforementioned properties of graphene. These include achieving good dispersion and interfacial properties between the graphene filler and the polymeric matrix. In the present work we report the thermal and mechanical properties of reduced graphene oxide/epoxy composites prepared via a facile, scalable and commercially-viable method. Electron micrographs of the composites demonstrate that the reduced graphene oxide (rGO) is well-dispersed throughout the composite. Although no improvements in glass transition temperature, tensile strength, and thermal stability in air of the composites were observed, good improvements in thermal conductivity (about 36%), tensile and storage moduli (more than 13%) were recorded with the addition of 2 wt% of rGO

Simulating Dispersion in the Evening-Transition Boundary Layer

This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this recordWe investigate dispersion in the evening-transition boundary layer using large-eddy simulation (LES). In the LES, a particle model traces pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent subgrid-scale motions. The LES is forced with both a sudden switch-off of the surface heat flux and also a more gradual observed evolution. The LES shows ‘lofting’ of plumes from near-surface releases in the pre-transition convective boundary layer; it also shows the subsequent ‘trapping’ of releases in the post-transition near-surface stable boundary layer and residual layer above. Given the paucity of observations for pollution dispersion in evening transitions, the LES proves a useful reference. We then use the LES to test and improve a one-dimensional Lagrangian Stochastic Model (LSM) such as is often used in practical dispersion studies. The LSM used here includes both time-varying and skewed turbulence statistics. It is forced with the vertical velocity variance, skewness and dissipation from the LES for particle releases at various heights and times in the evening transition. The LSM plume spreads are significantly larger than those from the LES in the post-transition stable boundary-layer trapping regime. The forcing from the LES was thus insufficient to constrain the plume evolution, and inclusion of the significant stratification effects was required. In the so-called modified LSM, a correction to the vertical velocity variance was included to represent the effect of stable stratification and the consequent presence of wave-like motions. The modified LSM shows improved trapping of particles in the post-transition stable boundary layer

Accessing the high-l frontier under the reduced shear approximation with k-cut cosmic shear

The precision of Stage IV cosmic shear surveys will enable us to probe smaller physical scales than ever before, however, model uncertainties from baryonic physics and non-linear structure formation will become a significant concern. The k-cut method - applying a redshift-dependent-cut after making the Bernardeau-Nishimichi-Taruya transform - can reduce sensitivity to baryonic physics; allowing Stage IV surveys to include information from increasingly higher-modes. Here we address the question of whether it can also mitigate the impact of making the reduced shear approximation; which is also important in the high-κ, small-scale regime. The standard procedure for relaxing this approximation requires the repeated evaluation of the convergence bispectrum, and consequently can be prohibitively computationally expensive when included in Monte Carlo analyses. We find that the k-cut cosmic shear procedure suppresses the w_{0}w_{a} CDM cosmological parameter biases expected from the reduced shear approximation for Stage IV experiments, when-modes up to 5000 are probed. The maximum cut required for biases from the reduced shear approximation to be below the threshold of significance is at k=5.37 h Mpc^{-1}. With this cut, the predicted 1σ constraints increase, relative to the case where the correction is directly computed, by less than 10% for all parameters. This represents a significant improvement in constraints compared to the more conservative case where only-modes up to 1500 are probed [A. Blanchard, (Euclid Collaboration), arXiv:1910.09273], and no k-cut is used. We also repeat this analysis for a hypothetical, comparable kinematic weak lensing survey. The key parts of code used for this analysis are made publicly available

Mapping Spatially Varying Additive Biases in Cosmic Shear Data

In this paper we address the challenge of extracting maps of spatially varying unknown additive biases from cosmic shear data. This is done by exploiting the isotropy of the cosmic shear field, and the anisotropy of a typical additive bias field, using an autocorrelation discrepancy map; which identifies significant non-Gaussian components of the map. We test this approach using simulations and find that the autocorrelation discrepancy map produces spatially varying features that are indicative of the additive bias field both in amplitude and spatial variation. We then apply this to the Dark Energy Survey Year 1 data, and find evidence for spatially varying additive biases of at most 0.002 on large-scales. The method can be used to empirically inform modelling of the spatially varying additive bias field in any cosmological parameter inference, and can act as a validation test for cosmic shear surveys

The mechanical properties and toughening mechanisms of an epoxy polymer modified with polysiloxane-based core-shell particles

AbstractAn epoxy resin, cured using an anhydride hardener, has been modified by the addition of pre-formed polysiloxane core-shell rubber (S-CSR) particles with a mean diameter of 0.18 μm. The glass transition temperature, Tg, of the cured unmodified epoxy polymer was 148 °C, and this was unchanged after the addition of the S-CSR particles. The polysiloxane rubber particles had a Tg of about −100 °C. Atomic force microscopy showed that the S-CSR particles were well-dispersed in the epoxy polymer. The addition of the S-CSR particles reduced the Young's modulus and tensile strength of the epoxy polymer, but at 20 °C the fracture energy, GIc, increased from 117 J/m2 for the unmodified epoxy to 947 J/m2 when 20 wt% of the S-CSR particles were incorporated. Fracture tests were also performed at −55 °C, −80 °C, and −109 °C. The results showed that the measured fracture energy of the S-CSR-modified epoxy polymers decreased significantly below room temperature. For example, at −109 °C, a fracture energy of 481 J/m2 was measured using 20 wt% of S-CSR particles. Nevertheless, this value of toughness still represented a major increase compared with the unmodified epoxy polymer, which possessed a value of GIc of 174 J/m2 at this very low test temperature. Thus, a clear fact that emerged was that the addition to the epoxy polymer of the S-CSR particles may indeed lead to significant toughening of the epoxy, even at temperatures as low as about −100 °C. The toughening mechanisms induced by the S-CSR particles were identified as (a) localised plastic shear-band yielding around the particles and (b) cavitation of the particles followed by plastic void growth of the epoxy polymer. These mechanisms were modelled using the Hsieh et al. approach [33,49] and the values of GIc of the S-CSR-modified epoxy polymers at the different test temperatures were calculated. Excellent agreement was found between the predictions and the experimentally measured fracture energies. Further, the experimental and modelling results of the present study indicated that the extent of plastic void growth was suppressed at low temperatures for the S-CSR-modified epoxy polymers, but that the localised shear-band yielding mechanism was relatively insensitive to the test temperature

The tensile fatigue behavior of a glass-fiber reinforced plastic composite using a hybrid-toughened epoxy matrix

ABSTRACT A thermosetting epoxy-polymer was modified by incorporating 9 wt.% of carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber microparticles and 10 wt.% of silica nanoparticles. The tensile fatigue behaviour at a stress ratio, R = 0.1 for both the neat (i.e. unmodified) epoxy-polymer and the hybridepoxy polymer was first investigated. The fatigue life of the hybrid-epoxy * Corresponding author: Tel. +91-80-2508 6310 ; Fax: +91-80-2508 6301 E-mail address: [email protected] (CM Manjunatha) 2 polymer was about six to ten times higher than that the neat-epoxy polymer. Secondly, the neat and the hybrid-epoxy resins were infused into a quasiisotropic lay-up, E-glass fiber fabric via a 'Resin Infusion under Flexible Tooling' (RIFT) set-up to fabricate glass-fiber reinforced-plastic (GFRP) composite panels. The tensile fatigue tests at a stress ratio, R = 0.1 were performed on both of these GFRP composites during which the matrix cracking and stiffness degradation were routinely monitored. The fatigue life of the GFRP composite increased by about six to ten times due to employing the hybrid-epoxy matrix, compared to the neat-epoxy matrix. Suppressed matrix cracking and a reduced crack propagation rate were observed in the hybrid-epoxy matrix, which resulted from the various toughening micromechanisms induced by the presence of both the rubber microparticles and silica nanoparticles. These factors were considered to contribute towards the enhanced fatigue life which was observed for the GFRP composite employing the hybrid-epoxy matrix

Surface functionalisation of nanodiamonds for human neural stem cell adhesion and proliferation.

Biological systems interact with nanostructured materials on a sub-cellular level. These interactions may govern cell behaviour and the precise control of a nanomaterial's structure and surface chemistry allow for a high degree of tunability to be achieved. Cells are surrounded by an extra-cellular matrix with nano-topographical properties. Diamond based materials, and specifically nanostructured diamond has attracted much attention due to its extreme electrical and mechanical properties, chemical inertness and biocompatibility. Here the interaction of nanodiamond monolayers with human Neural Stem Cells (hNSCs) has been investigated. The effect of altering surface functionalisation of nanodiamonds on hNSC adhesion and proliferation has shown that confluent cellular attachment occurs on oxygen terminated nanodiamonds (O-NDs), but not on hydrogen terminated nanodiamonds (H-NDs). Analysis of H and O-NDs by Atomic Force Microscopy, contact angle measurements and protein adsorption suggests that differences in topography, wettability, surface charge and protein adsorption of these surfaces may underlie the difference in cellular adhesion of hNSCs reported here

The tensile fatigue behaviour of a silica nanoparticle-modified glass fibre reinforced epoxy composite

Abstract An anhydride-cured thermosetting epoxy polymer was modified by incorporating 10 wt.% of welldispersed 20 nm diameter silica nanoparticles. The stress-controlled tensile fatigue behaviour at a stress ratio of R = 0.1 was investigated for bulk specimens of the neat and the silica-modified epoxy. The addition of the silica nanoparticles increased the fatigue life by about three to four times. The neat and the nanoparticle-modified epoxy resins were used to fabricate glass fibre reinforced plastic (GFRP) composite laminates by resin infusion under flexible tooling (RIFT). Tensile fatigue tests were performed on these composites, during which the matrix cracking and stiffness degradation was monitored. The fatigue life of the GFRP composite was increased by about three to four times due to the silica nanoparticles. Suppressed matrix cracking and a reduced crack propagation rate in the nanoparticle-modified matrix were observed to contribute towards the enhanced fatigue life of the composite containing the silica nanoparticles